The efficiency of a piezoelectric component is dependent on the values of the mechanical quality factor Qm and of the coupling coefficient KIJ. The coupling coefficient KIJ is a measure of the effectiveness of the conversion of electrical energy into mechanical energy, and vice versa. For many piezoelectric materials, the coupling coefficient K33 has the highest value. This corresponds to an arrangement in which the mechanical oscillations in the piezoelectric component are excited along the length of the piezoelectric base body. Furthermore, the electrodes are arranged at right angles with respect to the longitudinal direction of the piezoelectric base body. Moreover, the piezoelectric material is polarized in a longitudinal direction of the base body. In the majority of the already known variants of such a component, ceramic layers are arranged within the piezoelectric transformer parallel to the electrodes and are stacked one above another along the longitudinal direction of the piezoelectric base body. Therefore, the piezoelectric layers within the base body are likewise arranged at right angles with respect to the longitudinal direction of the base body. However, this so-called stack design of a piezoelectric transformer has some problems regarding production and electrical insulation between the input and output sides of the transformer. These transformers require a special sintering program in order to prevent possible detachment of the stack layers during the thermal treatment. If very good insulation between the input and output sides of the transformer is intended to be obtained, a special mechanical treatment after sintering is additionally required in order to ensure the exact dimensions of the piezoelectric component.
Another technology for the production of a piezoelectric transformer is described in “Piezoelectric Transformer Using Inter-Digital Internal Electrodes,” Masafumi Katsuno, Yoshiaki Fuda, IEEE Ultrasonics Symposium 1998, pages 897 to 900. The production process is explained, in particular, on page 899. The piezoelectric component comprises a plurality of ceramic layers which are arranged in a longitudinal direction of the piezoelectric base body and which are stacked one above another perpendicular to the longitudinal direction of the base body. The electrodes are arranged in the interior of the piezoelectric base body on the surfaces of the layers. This structure of a piezoelectric transformer corresponds to the construction of a multilayer ceramic capacitor and can thus be produced according to the conventional methods. This production process has advantages, in particular, with regard to the detachment of the layers during the thermal treatment and compliance with the correct dimensions.
The electrodes arranged on the surfaces of the layers jointly form a plurality of vertical electrodes arranged at a right angle with respect to the longitudinal direction of the piezoelectric base body. One problem with this construction, however, is the relatively high probability of a voltage flashover between electrodes in the input region and output region of the transformer which are arranged on the same surface of a layer. This problem occurs particularly in the case of polarization and generally at high voltages between the electrodes in the input and output regions. However, if the insulating regions are accordingly enlarged, the efficiency of the piezoelectric transformer decreases.
Consequently, there is a need for a piezoelectric component which has high insulation and thus a high flashover voltage between an input region and an output region of the piezoelectric component and which, at the same time, has a high efficiency, particularly for low power ranges.